1. Field of the Invention
The present invention relates to a developing apparatus which can be used with a forming apparatus such as an electrophotographic copying machine, an electrophotographic printer and the like.
2. Related Background Art
In image forming apparatuses of electrophotographic type or electrostatic type, an electrostatic latent image formed on an image bearing body such as an electrophotographic photosensitive body or an electrostatic recording dielectric body is visualized by a developing apparatus as a toner image.
As an example of such developing apparatuses, various dry one-component developing apparatuses have been proposed and put to a practical use. However, in all of such developing apparatuses, it is difficult to form a thin toner (one-component developer) layer on a developer bearing body.
Nowadays, since improvement in resolution and clearness of an image have been requested, development regarding method and apparatus for forming a thin toner layer is inevitable and some attempts have been proposed.
For example, as disclosed in Japanese Patent Application Laid-open No. 54-43038, an elastic blade (regulating member) made of metal or rubber abuts against a developing sleeve (developer bearing body) so that, by passing toner through an abutment area between the elastic blade and the developing sleeve to regulate the toner, a thin toner layer is formed on the developing sleeve and adequate triboelectricity is applied to the toner by friction generated in the abutment area.
In this case, when nonmagnetic toner is regulated by the elastic blade, a toner supplying member for supplying the toner onto the developing sleeve must be provided additionally. The reason is that, although magnetic toner can be supplied onto the developing sleeve by a force of a magnet disposed within the developing sleeve, the nonmagnetic toner cannot be supplied by such a magnetic force.
Now, an example of a conventional color laser printer as a conventional multi color electrophotographic image forming apparatus will be described with reference to FIG. 6.
Within a main body of an image forming apparatus, there are disposed an image bearing body unit 101, a laser scanner portion 105, a developing unit 106 of rotary type, a transfer unit 107, a sheet feeding unit 108 and a fixing device 109 and the like.
The image bearing body unit 101 includes an image bearing body (electrophotographic photosensitive drum) 102 rotated in an counter-clockwise direction shown by the arrow, a charging device 103 and a cleaning device 104 and constitutes a process cartridge detachably attachable to the main body of the image forming apparatus.
The developing unit 106 includes four developing devices 106Y, 106M, 106C, 106B containing four color (yellow, magenta, cyan and black) toners. The four color developing devices are rotatably mounted on a rotary 106b rotated in a clockwise direction around a shaft 106a . The shaft 106a is provided with a revolution gear around which rotation gears are meshed, so that, in synchronism with the movement of the rotation gears, the developing devices 106Y, 106M, 106C, 106B are rotated, thereby maintaining the postures of the developing devices constant.
The developing devices 106Y, 106M, 106C, 106B are constituted as a developing cartridge detachably attachable to the rotary 106b.
The transfer unit 107 mainly includes a transfer drum 107a rotated in a clockwise direction shown by the arrow, so that a transfer material P fed from the sheet feeding unit 108 can be wound around the transfer drum 107a and be conveyed by the transfer drum.
The sheet feeding unit 108 includes a sheet feeding cassette 108a disposed at a lower part of the main body of the image forming apparatus, a sheet feeding roller (pick-up roller) 108b for feeding out the transfer materials P from the sheet feeding cassette, and a sheet path 108c including a one sheet separation and feed roller, a turn roller and registration rollers, so that the transfer material P is fed to the transfer drum 107a of the transfer unit 107 at a predetermined control timing.
When the rotating image bearing body 102 of the image bearing body unit 101 is subjected to uniform charging treatment effected by the charging device 103 with a predetermined polarity and potential and laser scan exposure L (corresponding to predetermined image information) effected by the laser scanner portion 105, an electrostatic latent image corresponding to the predetermined image information is formed on the peripheral surface of image bearing body.
The electrostatic latent image is developed as a toner image by a predetermined developing device of the developing unit 106. In image formation, among the developing devices 106Y, 106M, 106C, 106B of the developing unit 106, the developing device corresponding to the latent image is stopped at a position opposed to the image bearing body 102, and the developing device is pressed against the image bearing body 102 by a pressurizing mechanism so that a developing sleeve 106S is positioned to be opposed to the surface of the image bearing body 102 with a small gap therebetween. In the development, bias is applied to the developing sleeve 106S and the developing sleeve is rotated, thereby developing the latent image formed on the image bearing body 102 as a toner image. The toner image is transferred onto the transfer material P wound around the peripheral surface of the transfer drum 107a.
The cleaning device 104 serves to remove residual toner from the surface of the image bearing body after the transferring operation.
In case of a full-color image, four color (yellow, magenta, cyan and black) toner images successively formed on the image bearing body 102 are successively transferred onto the same transfer material P wound around the peripheral surface of the transfer drum 107a.
The transfer material P to which the toner images were transferred is separated from the surface of the transfer drum 107a and then is introduced into the fixing device 109, where the toner images are melted and mixed by receiving permanent fixing to form a full-color toner image. Thereafter, the transfer material is discharged out of the image forming apparatus.
FIG. 7 is an enlarged schematic sectional view of the developing apparatus (developing cartridge). The developing devices 106 (Y, M, C, B) have the same constructions and each has a developing container 91 containing nonmagnetic toner (one-component developer) T, a rotating developing sleeve (developer bearing body) 92 disposed at an opening portion of the developing container, an elastic regulating blade 93 abutting against the developing sleeve with the interposition of the developer, an elastic roller (developer supplying member for supplying the developer to the developing sleeve) 94, and a toner feed mechanism 95 and the like.
More specifically, in this conventional developing apparatus, within the developing container 91 containing the nonmagnetic toner (one-component developer) T, there is provided the elastic roller 94 using foam material such as polyurethane foam or sponge or a fur brush which abuts against the developing sleeve 92 at a position upstream of the elastic regulating blade 93 in a rotational direction of the developing sleeve 92, so that, by rotating the elastic roller 94 in a direction shown by the arrow F, the toner T is supplied onto the developing sleeve 92.
The elastic regulating blade 93 comprises an elastic blade portion and a support metal plate for supporting the blade portion, and the support metal plate is pinched between a holding metal plate 68 of the developing container 91 and a pressing metal plate 69. The holding metal plate 68, elastic regulating blade 93 and pressing metal plate 69 are positioned by a positioning boss 27b integral with the developing container 91.
The toner T supplied to the developing sleeve 92 by the rotation of the elastic roller 94 is sent to an abutment area between the elastic regulating blade 93 and the developing sleeve 92 to form a thin layer as the developing sleeve 92 is rotated, or preparation or development of the electrostatic latent image formed on the photosensitive body (image bearing body) 102.
Residual toner remaining on the developing sleeve 92 (which was not consumed) is brought to an abutment area between the developing sleeve 92 and the elastic roller 94 by further rotation of the developing sleeve 92, where the residual toner is scraped by the elastic roller 94, and new toner is supplied onto the developing sleeve 92 by the rotation of the elastic roller 94. This operation is repeated.
Further, in this case, when metallic material is used to form the developing sleeve 92, the regulating blade 93 formed from a thin metal plate is not preferable from a viewpoint of wear of the developing sleeve 92, and, in order to obtain a good thin toner layer, rubber material such as urethane or silicone must be used.
With this arrangement, a thin layer of the nonmagnetic toner T can be effectively formed on the developing sleeve 92 effectively.
However, when toner including spherical and smooth particles (toner having shape factor SF-1 of 100 to 180 and shape factor SF-2 of 100 to 140) obtained by recent further improvement is utilized, if the conventional developing apparatus is used, depending upon the positional relationship between the elastic regulating blade 93 and the developing sleeve 92, passing-through of the toner may occur and/or developing ability may be worsened.
To avoid this problem, a tolerance of positioning of the elastic regulating blade with respect to the main body of the image forming apparatus must be severely selected to eliminate positional deviation. Thus, costs of the elastic regulating blade 93 and the developing container 91 and elastic regulating blade holding metal plate 68 to which the elastic regulating blade is attached are increased greatly, thereby making the entire developing apparatus more expensive.
Further, to solve such a problem, although it is considered that, after attachment, the elastic regulating blade 93 is adjusted to improve the positioning accuracy, in effect, since the support metal plate for the elastic regulating blade 93 is formed from a thin metal sheet, when the support metal plate is moved during the adjustment, the metal plate will be deformed, thereby making the adjustment impossible.